rtnetlink: Add public interface parser

This will be used by the rtnetlink server to parse new links.

Change-Id: Ibc0abc12ca58b78ffc22ac6f75822853d4b7bdc8
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/rtnetlink.hpp b/src/rtnetlink.hpp
index 2862143..5436e9d 100644
--- a/src/rtnetlink.hpp
+++ b/src/rtnetlink.hpp
@@ -8,6 +8,8 @@
 namespace phosphor::network::netlink
 {
 
+InterfaceInfo intfFromRtm(std::string_view msg);
+
 std::optional<std::tuple<unsigned, InAddrAny>>
     gatewayFromRtm(std::string_view msg);